From <www.ukraine.online.com.ua>:
"The Constitution states that the national symbols of
Ukraine shall be the National Flag, the National Emblem and the
National Anthem.
The Ukrainian flag consists of two horizontal stripes of equal
width. The top is blue, the bottom - yellow. Blue and yellow, the
colors of the sky, mountains, streams, and golden fields have
symbolized Kyivan Rus' long before the introduction of
Christianity. With the acceptance of Christianity, blue and gold
were incorporated into church symbolism. After the Mongol-Tatar
invasion in the 1200's the use of blue/gold was interrupted, to
be revived again in church ornaments and city crests some time
later. The emblem of the city of Myrhorod, for example, was a
gold trident over a blue background. Another city, Pryluky, used
the head of an ox in gold over a blue background as its insignia.
And in Lubny, the city emblem pictured a hand holding a golden
mace over a blue background. The banners of the Cossacks (17th
Century) were blue with gold stars, a gold cross, or with
pictures of saints rendered in gold.
The blue and yellow flag as the national flag of Ukraine by the
Supreme Rada in 1992."Dov Gutterman, 10 July 2000

The blue-yellow flag was firstly displayed in Lviv (Lvov,
Lemberg) in 1848. Orenburg, for example, have blue-yellow CoA
too, But it is not in Ukraine. Banners of Cossacks were
different: blue, red, dark-red, green and other.Victor Lomantsov, 10 July 2000

In Sweden there is a story going around, stating that the blue
and yellow of Ukraine come from the blue and yellow of Sweden.
When King Carl XII of Sweden (he was king 1697-1718) went to war
against Peter the Great of Russia, he made allies with the
Ukranians, who wanted sovereignity from Russia. The Ukrainians
should therefore have taken up the colours of Sweden as their
colours. However, I don't know if there is any truth in this
story.Elias Granqvist, 10 July 2000

According to Album 2000 [pay00]
- National Flag and Naval Jack (CSW/CS- 2:3) - Light blue over
yellow bicolour.Željko Heimer, 10 May 2003

Ukrainian state flag was adopted on January 28, 1992 by Decree
No 2067-XII of the Verkhovna Rada (=Supreme Council =
Parliament). Other dates (January 21, 1992; September 3, 1996)
are incorrect. Now the Ministry of Justice prepared new project
of law about the State symbols of Ukraine. But it isn't still
adopted.
Resolution of September 4, 1991 gave only possibility to use
Ukrainian National (blue and yellow) flag during the official
ceremonies - before the addopting of new State flag. Please note,
in former USSR we had the term "State flag". So, in
that case "National flag" was not a "State".
But final Decree, named "About the State flag of
Ukraine" was adopted on January 28, 1992. Number of Decree
is 2067-XII. Official publication in "Vidomosti Verkhovnoyi
Rady Ukrayiny" (Official bulletin of the Supreme Council of
Ukraine) was in No. 19 (1992), article 257.
4 September 1991 is the date when blue and yellow flag was first
flew at the building of the Supreme Council in Kyiv (together
with flag of the former Ukrainian SSR). But Decree of the
Presidium of Supreme Council about using of blue and yellow flag
was adopted on September 18, 1991 (No 1567-XII). Literally in
text: "Allow to use blue and yellow flag in all official
ceremonies untill the adopting of Constitution of Ukraine".
This Decree doesn't include ratio or other details of flag.
De-facto, it abolished former State flag of the Ukrainian SSR,
and proclaimed a blue and yellow as temporary official flag.
Decree of January 28, 1992 proclaimed a blue and yellow as the
State flag of Ukraine.Andriy Grechylo, 24 March 2004

Darker or lighter colours of Ukrainian flag haven't any
political significance. According the legislations we have SYNIY
(blue) and ZHOVTYI (yellow) colours, but our society also accept
darker (for example - marine blue) or lighter (ligth blue)
colours.Andriy Grechylo, 28 November 2004

In his role as the current President of the Council of
Ministers of the European Union, British Prime Minister Tony
Blair has been touring eastern European capitals to try to
resolve the problems with the E.U. budget. A report on 'The
World' last night on BBC4 showed him speaking at a meeting in a
location which wasn't specified, but, from the panel on the wall
behind him, was clearly connected with Ukraine if not actually in
that country. I was struck by the colours of the Ukrainian flag
next to the E.U. one in this photo.
There may indeed be no political significance to the colours, at
least in an internal Ukrainian party sense, but I can't help
feeling that their similarity to the dark blue and gold of the
E.U. flag isn't a coincidence!Andre Coutanche, 2 December 2005

The protocol manual for the London 2012 Olympics (Flags and Anthems Manual London 2012) provides recommendations for
national flag designs. Each NOC was sent an image of the flag,
including the PMS shades, for their approval by LOCOG. Once this was
obtained, LOCOG produced a 60 x 90 cm version of the flag for further
approval. So, while these specs may not be the official, government,
version of each flag, they are certainly what the NOC believed the
flag to be.

The Open Media Research Institute reported that on 3 September
1996 the Ukrainian Parliament (Verkhovna Rada) had approved the
country's national symbols as specified by the constitution
[OMRI, #171, 1996]. Parliament also decided to organise a
competition on the design of the state arms and the words of the
national anthem. The 'tryzub' (trident) is the state arms, and
the competition will decide the details of the design. The new
constitution was adopted by Parliament 28 June 1996 (the date was
declared a national holiday) and only confirmed the national
symbols that were already in use [OMRI, #204, 1996]. OMRI offered
no details on the action of the parliament, nor did they give any
descriptions of the symbols. Article 20 of the constitution
states that the 'The description of the state symbols of Ukraine
and the order of their use is determined by law' [IFES]:

"ARTICLE 20.
The state symbols of Ukraine are the State Flag of Ukraine, the
State Emblem of Ukraine and the State Anthem of Ukraine. The
State Flag of Ukraine is a banner made from two equal horizontal
blue and yellow fields. The Great State Emblem of Ukraine shall
be determined in accordance with the Small State Emblem of
Ukraine and the Emblem of the Zaporiz'ke Viys'ko (Zaporizhzhya
Cossacks Army) by law, which shall be adopted by no less than
two-thirds of the Constitutional membership of the Verkhovna Rada
of Ukraine. The main element of the Great Emblem of Ukraine is
the Sign of the State of Prince Volodymyr the Great (the Small
State Emblem of Ukraine). The State Anthem of Ukraine is the
national anthem with the music of M.Verbytskiy and words,
confirmed by law, which shall be adopted by no less than
two-thirds of the constitutional membership of the Verkhovna Rada
of Ukraine. The description of the state symbols of Ukraine and
the order of their use is determined by law, adopted by no less
than two-thirds of the constitutional membership of the Verkhovna
Rada of Ukraine. The capital of Ukraine is City of Kyiv."

Ukraine declared independence from the USSR on 24 August 1991.
MPs celebrated the event by carrying a huge light blue and yellow
flag through the assembly hall of the Parliament [Ukrainian
Weekly, 1996]. Ukrainians approved the independence proclamation
in a referendum held 1 December 1991. Provisional legislation [W.
Smith, 1992] concerning the flag was adopted on 4 September 1991,
with opposition from the Communists. This legislation therefore
also made the Soviet era flag official, and the two flags were
hoisted side by side (even on the same flag pole). The light blue
over yellow flag was in proportions 1:2. The situation was
changed 21 January 1992, when the light blue and yellow flag
became the only flag of Ukraine. The proportions of the flag were
then set to 2:3. The trident arms were adopted on 19 February
1992 [W. Smith, 1992].

I saw today in German TV ZDF this variation of Ukrainian
national flag with the national symbol in the left upper corner.
The flag was on a demonstration against the "results"
of the presidental election.J. Patrick Fischer, 24 November 2004

Today I saw on TV the 1:2-version of this flag. The flag of
yesterday has really 3:5. The yellow of the logo is the same as
the yellow of the stripe.J. Patrick Fischer, 25 November 2004

This variation of Ukrainian flag was in project of the New
Constitution (1997). But finally the Parliament (Verkhovna Rada)
accepted our proposal - without image in the left upper corner.
So, some people use variations of national flag (with Trident at
shield or with Trident) during holidays, meetings etc.Dr.Andriy Grechylo, 25 November 2004

I have taken a couple of photos of the Ukrainian demonstration in Munich
on 7 Feb 2015.
(https://groups.yahoo.com/neo/groups/FLAGS/photos/albums/730714280)

In addition to the plain bicolour there were several versions of the
national flag either with the plain trident or with the trident in a shield: